1. Field of the Invention
The present disclosure generally relates to optics and, more particularly, to a wavefront aberration measuring method and a wavefront aberration measuring device that measure wavefront aberrations of optical systems. In particular, the wavefront aberration measuring method and the wavefront aberration measuring device may be used for measurement of a wavefront aberration of an optical system when the optical system has a large wavefront aberration.
2. Description of the Related Art
The Shack-Hartmann method is known as a method of measuring a wavefront aberration of an optical system. The Shack-Hartmann method forms a plurality of spot images by causing light, which is transmitted through a test optical system, to be incident on a lenslet array, reconfigures a transmitted wavefront of the test optical system based on the positions of the plurality of spot images, and hence measures a wavefront aberration.
However, if an optical system having a large aberration is measured by the Shack-Hartmann method, a distortion and a shift may be generated at a spot image in a peripheral portion of a light receiving element, and position information of the spot image may not be correctly obtained. If a wavefront aberration is calculated on the basis of the incorrect position information, measurement accuracy may be decreased.
Regarding the problems, Japanese Patent Laid-Open No. 2004-317376 discloses a method of not using position information of a spot image formed in the outermost peripheral portion of a light receiving element when a wavefront is reconfigured. Also, Japanese Patent Laid-Open No. 2004-61238 discloses a method of not using position information of a spot image when a wavefront is reconfigured if a displacement amount of the position of the spot image with reference to a predetermined reference position exceeds a predetermined value.
However, with the wavefront aberration methods of any of Japanese Patent Laid-Open No. 2004-317376 and No. 2004-61238, the position information of the spot image formed in the peripheral portion of the light receiving element is not used although the position information is particularly important for calculating a large wavefront aberration. Hence, measurement accuracy for a wavefront aberration is not sufficient. Also, since the position information of the spot image used when the wavefront is reconfigured is decreased, the measurement accuracy for a wavefront aberration is decreased.
To accurately measure the wavefront aberration of the test optical system having a large wavefront aberration, the position information of the spot image formed in the peripheral portion of the light receiving element has to be accurately detected.